1. Field of the Invention
The present invention relates to an improved method for fabricating semiconductor devices and, more particularly, an improved method for forming salicide structures during semiconductor device manufacturing processes using nickel, a nickel alloy, or another metal or metal alloy capable of forming silicides at lower temperatures, e.g., less than about 725° C., to form the salicide layer and modifying the heat treatment sequence to reactivate previously deactivated dopant atoms.
2. Description of the Related Art
As the integration density of semiconductor devices continues to increase and the critical dimensions associated with such devices continue to decrease, there has been a corresponding increase in interest in identifying materials and processes for producing interest in low resistance materials to maintain or reduce signal delay. Silicide and salicide (self-aligned silicide) materials and processes have been widely used to lower the sheet resistance and contact resistance for the gate conductor and source/drain regions of MOS devices.
A number of metals, including tungsten, tantalum, zirconium, titanium, hafnium, platinum, palladium, vanadium, niobium, cobalt, nickel and various alloys of such metals have been used to form silicide layers on semiconductor devices. For gate lengths below about 100 nm, however, conventional salicide processes and materials tend to experience a variety of difficulties including opens, residues and layer non-uniformity, resulting at least in part from agglomeration within the silicide material layer.
These difficulties tend to be exacerbated by the high-temperature processing required to react most metal(s) with silicon to form the desired silicide layers. The high temperature anneals required also raise concerns regarding the impact of the silicide annealing process(es) on the thermal budget for the devices being manufactured. For example, when cobalt is used to form the silicide, the initial stoichiometry of the silicide may be generally represented as CoSi, but as the annealing process continues, particularly at higher temperatures, the silicide tends to incorporate an increasing amount of silicon and approaches a composition more closely represented as CoSi2. For devices having gate lengths below about 100 nm, however, the second high temperature silicidation used in conventional Co salicide processes tends to induce agglomeration within the silicide material layer, increasing the degree of non-uniformity within the layer and tending to degrade the performance of the resulting devices.
A conventional salicide process sequence is illustrated in FIG. 1, wherein, after forming a gate structure (S10), a first ion implant process is used to form a lightly-doped drain (S20), gate spacers are formed (S30) adjacent the gate electrode sidewalls, a heavier source/drain (S/D) implant (S40) is used to form the S/D regions in the substrate, and an activation anneal (S50) is conducted to activate a portion of the implanted dopant(s) to modify the performance of the implanted regions of the substrate. After the dopant activation anneal, a silicide blocking layer is formed (S60), a silicidation metal or metal alloy layer is formed and a salicide pattern is formed by reacting the silicidation metal(s) with exposed silicon surfaces, after which the remainder of the silicidation metal(s) are removed (S70). Once the salicide pattern has been formed, the unreacted portion of the silicidation metal(s) may be removed and an interlayer dielectric formed (S80) to begin the metallization process.
Nickel is an attractive metal for forming silicides because the annealing process required to form the desired silicide may be conducted at a relatively low temperature, e.g., below about 550° C. Depending on the reaction conditions, nickel can react with silicon to form dinickel monosilicide, Ni2Si, nickel silicide, NiSi, or nickel disilicide, NiSi2, as the silicidation product. Using annealing temperatures greater than about 550° C. tends to increase the formation of the most resistive nickel-disilicide NiSi2 and a corresponding increase in the silicon consumption and are, therefore, generally avoided. Nickel silicide, NiSi, however, can be preferentially formed at lower temperatures and provides the lowest sheet resistance of the three nickel silicide phases. Due to the low silicidation temperature, NiSi exhibits a decreased tendency to agglomerate and form a silicide layer in which the sheet resistance is generally independent of the device dimensions, increasing its utility for lowering the resistance of fine line structures.